Project Summary: Domoic Acid (DA) is a marine-based toxin produced by the diatom Pseudo-nitzschia. Based upon nearly 100 Canadian cases of acute toxicity in 1987, a regulatory limit for DA (20 ppm) was established for shellfish consumption. This has been protective against acute cases of Amnesic Shellfish Poisoning, seizures, coma, or death in the U.S. However, recent longitudinal cohort studies of coastal WA Native Americans (NA) provide new evidence that current criteria are not protective against chronic toxicity. A decrease in memory function in adult high consumers over time and psychomotor slowing in perinatally exposed children occurs at much lower doses. Thus, consumption advisories are in place for vulnerable members of the Makah, Quileute, and Quinault Nations in Washington State. In response to this, an important immediate question remains for scientists, epidemiologists and Washington Department of Health officials: What are the implications of these findings for non-NA razor clam consumers? The objective of this study is to work with the Washington Departments of Health (WDOH) and Fish and Wildlife to provide an immediate response to new data and concerns related to the potential human health threat of chronic exposure to low levels of domoic acid (DA) via razor clam consumption. Toward this end, the development of a risk assessment framework for non-NA razor clam consumers is proposed. Specific aims include 1) developing provisional chronic oral reference doses (RfDo) for DA, building upon the toxicity data from the NA tribes; 2) characterizing the exposure (and associated risk factors) of 1100 non-NA razor clam harvesters through harvesting beach surveys and 3) identifying areas/conditions that represent the highest risk for development of chronic toxicity (based on DA levels and consumption patterns) using geospatial analyses. These risk assessment studies will be completed over the next 12-24 months. An active research partnership with the Washington Department of Health will speed the adoption, use and translation of the findings into a form useful to support regulatory decision making.